A floating vehicle door pressure detector comprises a detection cylinder for contacting and sensing door pressure and a handle fixed to the detection cylinder. One end of the detection cylinder is a fixed end equipped with a pressure sensor, and the other end is a floating end which is axially aligned with the fixed end and can be elastically stretched in an axial direction. The floating end is axially retracted under push of the door pressure and transmits the door pressure to the sensor. By using the floating vehicle door pressure detector of the invention, a detection process simulates a stress process of deliberate door clamping, vehicle door pressure data is more real and effective, a pressure of a closed door distance which is within a range of 100 to 115 mm is safely valued, effective and reliable test data is provided, a passenger is ensured not to get injured when the door clamps the passenger, and safety of rail vehicle door opening and closing is improved. The invention also relates to a rail vehicle door pressure detecting method.